MariaDB MaxScale 2.3.0 Release Notes -- 2018-10-09

MariaDB MaxScale 2.3.0 Release Notes -- 2018-10-09

Release 2.3.0 is a Beta release.

This document describes the changes in release 2.3.0, when compared to release 2.2.

For any problems you encounter, please consider submitting a bug report at Jira.

Changed Features

maxadmin list threads

Maxadmin list threads now shows the descriptor counts and load of the MaxScale worker threads. For details, please consult the maxadmin documentation.

MaxCtrl create monitor

The create monitor command now accepts a list of key-value parameters that are passed to the monitor as the last argument. This allows creation and configuration of monitors in one command.


The default value of query_retries was changed from 0 to 1. This turns on failure tolerant queries for monitors and authenticators which prevents failures due to network problems. A single reconnection attempt is made to keep responsiveness high even with default values.

Session Command History

The readwritesplit session command history is now enabled by default but it is limited to a total of 50 distict session commands. This default allows most sessions to leverage the newly improved reconnection mechanism without having to explicitly enable the history. When the limit of 50 commands is exceeded, the session command history is disabled. This makes it possible to use pooled connections by default without having to explicitly disable the history (this was the case with pre-2.1 versions of MaxScale).

The way that the history is stored has also changed. Instead of storing all session commands, each session only stores the first and last execution of each command. This way the history is compressed into a compact representation while still retaining the relative order of each command.

To keep the old functionality, add disable_sescmd_history=true to the service definition.

Cache Filter

The rules can now be expressed using a JSON array containing rule objects, which makes it easier to express more complex rules. Please see the Cache documentation for details.

Masking Filter

By default the masking filter rejects statements that use functions on conjuction with columns that should be masked. Please see the Masking Filter documentation for details.

router_options in Binlogrouter

The use of router_options with the binlogrouter module is deprecated in MaxScale 2.3 and will be removed in a subsequent release. The router_options should be converted into separate parameters.


The thread_stack_size configuration parameter is ignored and has been deprecated. If you need to explicitly set the stack size, do so using ulimit -s before starting MaxScale.

ssl for Servers and Listeners

The ssl parameter now accepts boolean values ìn addition to the old required and disabled values.


MariaDBMonitor has undergone several changes listed briefly below. Please see MariaDBMonitor documentation for more details.

JSON diagnostics output changed

The data in the diagnostic output of the REST-API has changed, with some fields removed and others added.

Master detection

The monitor is now less likely to suddenly change the master server, even if another server has more slaves than the current master. The DBA can force a master reselection by setting the current master read-only, or by removing all its slaves if the master is down.

Only one server can have the Master status flag at a time, even in a multimaster setup. Others servers in the multimaster group are given the Relay Master and Slave status flags.

Switchover new master autoselection

The switchover command can now be called with just the monitor instance name as parameter. In this case the monitor will automatically select a server for promotion.

Replication lag detection

The replication lag measurement now simply reads the Seconds_Behind_Master-field of the slave status output of slaves. The slave calculates this value by comparing the time stamp in the binlog event the slave is currently processing to the slave's own clock. If a slave has multiple slave connections, the smallest lag is used.

Low disk space detection, automatic switchover

With recent MariaDB Server versions, the monitor can check the disk space on the backends and detect if the server is running low. The monitor can be set to automatically switchover a master low on disk space. Slaves can be set to maintenance mode. Disk space is also considered when selecting a new master for promotion. See switchover_on_low_disk_space and maintenance_on_low_disk_space for more information.

Replication reset feature

The reset-replication monitor command deletes all slave connections and binary logs, and then sets up replication. Useful when data is in sync but gtid:s are not.

Scheduled events handling in failover/switchover/rejoin

Server events lauched by the event scheduler thread are now handled during cluster modification operations. See handle_server_events for more information.

Unused parameters

The following parameters are unused and are ignored if set: - mysql51_replication MySQL5.1 is no longer supported. - multimaster The monitor now always detects multimaster setups. - allow_cluster_recovery Now always on. - detect_replication_lag Lag detection no longer writes to databases so it is always on.

Dropped Features

log_to_shm parameter and --log=shm option

The following commands no longer create the log files in shared memory and will be ignored. MaxScale will behave as if --log=file was provided when --log=shm is used. The log_to_shm parameter is ignored. Both the parameter and the optino value are deprecated and will be removed in a later relesae.

Logs can still be created in shared memory by pointing logdir to /dev/shm.

Configuration Reloading

The deprecated maxadmin reload config command has been removed.

router_options in Avrorouter

The use of router_options with avrorouter was deprecated in MaxScale 2.1. In MaxScale 2.3, the use of router_options is no longer supported and the options should be given as parameters instead.

router_options in readwritesplit

The use of router_options with readwritesplit, which was deprecated in MaxScale 2.2.0, has been removed in MaxScale 2.3.0.


The CDC protocol no longer accepts the QUERY-LAST-TRANSACTION and QUERY-TRANSACTION commands. They were removed due to the addition of the REST API that provides the same information in a more easy to process format.

New Features

Binlog Router

If the binlog router is replicating from a Galera cluster it is now possible to specify secondary masters that the binlog router automatically will switch to, in case the primary master for some reason goes down. Please see the binlog router documentation for details.


There is now a new hint last that will cause a query to be routed to the same server the previous query was routed to.

Backend Connection IDs

The backend connection IDs are now shown in the show sessions output of MaxCtrl.

Comment Filter

With the comment filter it is possible to prepend statement received with a comment before it is sent further to a server. Please see the comment filter documentation for more details.

Query Classifier Cache

The query classifier now caches the results of each classification which significantly improves performance of workloads that require query classification. The default cache size limit is 40% of total system memory.

Read the configuration guide for more information about the details of the query classifier cache and how to configure it.

Runtime Configuration of the Cache

With the variables @maxscale.cache.use and @maxscale.cache.populate it is now possible for a client to specify whether the cache should be used and/or populated. Please see the Cache documentation for details.

User Specified Syslog Facility and Level for Authentication Errors

It is now possible for the end user to specify the syslog facility and level for authentication errors. Please see the configuration guide for details.

Named Server Filter

The source parameter can now contain a list of comma separated addresses.

Table Family Sharding

The SchemaRouter is now capable of table family sharding. Please see the SchemaRouter documentation for details.

Throttle filter

The throttlefilter replaces and extends on the limit_queries functionality of the Database Firewall filter.


A set of new features have been added to readwritesplit.


The transaction_replay parameter enables replaying of transactions if a master server is lost mid-transaction. This allows transparent replacement of master servers with a minimal amount of failed transactions.


With the master_reconnection parameter, if the connection to a master server is lost or the master server changes, readwritesplit can now reconnect seamlessly to the master server without losing the session state.


The delayed_retry parameter allows queries to be automatically retried if their execution is interrupted.


The causal_reads parameter enables distributed consistent reads with MariaDB version 10.2 and newer.


The optimistic_trx parameter enables optimistic transaction execution. This parameter controls whether normal transactions (i.e. START TRANSACTION or BEGIN) are load balanced across slaves. If the transaction tries to modify a row, it is migrated to the master and rolled back on the slave.

Adaptive Routing

A new load balancing method, ADAPTIVE_ROUTING, was added. It uses the average query response time to distribute the load so that it is optimal on all servers.


For more detailed information about the features of MaxCtrl, see the documentation or the output of maxctrl help.

Interactive Mode for MaxCtrl

MaxCtrl can now be started in an interactive mode similar to MaxAdmin. This makes use of passwords more convenient as they have to be input only once and they are cached for the duration of the session.

Draining Server Connections

The new drain server drains the server of connections by first removing it from all services after which it waits until all connections are closed. When all connections are closed, the server is put into the maintenance state and added back to all the services where it was removed from.

Resultset Concatenation Router

A new experimental router module, cat, was added to the maxscale-experimental package. The cat router is a special router that concatenates result sets. For more information and an explanation on how the router works, read the cat documentation.

REST API Additions

Creation of Services and Filters at Runtime

The REST API and MaxCtrl now support the creation and destruction of services and filters at runtime. This also means that the filters of a service can now be modified at runtime. Refer to the REST API and MaxCtrl documentation for more details.

Alteration of Routers

The router parameters of services can now be altered at runtime. Currently only the readwritesplit router implements this feature.

Binlog Filtering

The binlogfilter is a filter module that allows the client side stream of binlogs to be filtered. It is designed to be used with the binlogrouter.

This allows conditional replication similar to replicate_do_table but with full PCRE2 compliant match/exclude functionality. For more information, refer to the binlogfilter documentation.

Network Traffic Buffering

The new writeq_high_water and writeq_low_water parameters allow network traffic to be throttled if it exceeds the highwater mark. This can be used to prevent MaxScale from buffering too much data in memory if the client is not reading results fast enough.

Bug fixes

Here is a list of bugs fixed in MaxScale 2.3.0.

Known Issues and Limitations

There are some limitations and known issues within this version of MaxScale. For more information, please refer to the Limitations document.


RPM and Debian packages are provided for the Linux distributions supported by MariaDB Enterprise.

Packages can be downloaded here.

Source Code

The source code of MaxScale is tagged at GitHub with a tag, which is identical with the version of MaxScale. For instance, the tag of version X.Y.Z of MaxScale is X.Y.Z. Further, master always refers to the latest released non-beta version.

The source code is available here.


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